Numerous means have been sought to improve the fuel-efficiency of moving bodies, and especially moving bluff bodies, by reducing their aerodynamic drag. In the field of surface transportation, and particularly in the long-haul trucking industry, even small improvements in fuel efficiency can reduce annual operating costs significantly. It is therefore advantageous in the design of a vehicle to reduce drag forces; thereby increasing the aerodynamic properties and efficiency of the vehicle.
The over-the-highway cargo hauling tractor-trailer combination is one vehicle that experiences excessive aerodynamic drag. Generally described, tractor-trailer combinations 18 typically include a tractor 20 having a so-called fifth wheel by which a box-like semi-trailer 24 may be attached to the tractor 20 by an articulated connection for transportation of the semi-trailer 24, as shown in FIG. 1. By providing the articulated connection, a space or gap 28 is formed between the rear wall 32 of the tractor cab and the forward wall 44 of the semi-trailer 24. It is well known that this gap 28, or the gap between succeeding trailers (not shown) of a tractor trailer combination causes wake regions and, as a result, pressure drag.
Previous investigations of aerodynamic drag of tractor-trailer combinations resulted in widespread adoption of air deflectors mounted on tractor cabs and/or trailer bodies, and wholly redesigned tractors that utilize aerodynamic fairings to gradually increase the relatively small frontal area of the tractors to match, and to blend smoothly with, the larger cross-section of typical trailers, in an attempt to deflect air efficiently across the gap between cab assemblies and trailer bodies. Current air deflectors and fairings help guide the airstream around the front of tractor-trailer combinations and/or smooth the air flow over the gap between the articulated bodies, thereby reducing aerodynamic drag and improving fuel efficiency. Please see U.S. Pat. No. 4,021,069 to Hersh, U.S. Pat. No. 2,514,695 to Dempsey, U.S. Pat. No. 4,210,354 to Canning and U.S. Pat. No. 3,971,586 to Saunders, which are typical of trailer-mounted nose cone assemblies, and U.S. Pat. No. 4,245,862 to Buckley and U.S. Pat. No. 4,904,015 to Haines, which are typical of cab mounted deflectors or fairings. While in some instances these systems reduce the effective gap between bodies, such gap reduction is incidental and often there is still a significant amount of drag caused by the gap. Thus, aerodynamic drag reduction across the air gap between adjacent articulated tractor-trailer combination bodies is only partially achieved by fairings and deflectors.
Another approach, which has been the subject of numerous patents but has not been widely adopted in the trucking industry, is to attempt to span or seal the gap between vehicle bodies by fairings, panels, resilient bodies or the like. Please see U.S. Pat. Nos. 4,611,847, 4,397,496, 4,343,506, 4,141,755, 4,036,519, 3,834,752, 3,711,146, 3,425,740, 2,101,793 and D238,161, which disclose articulated tractor-trailer combinations having side and top structures that extend across the gap between the cab assembly and the trailer body to reduce the vehicle's aerodynamic drag.
These prior art mechanical gap-spanning systems, however, tend to suffer from problems of reliability and operating inconvenience. Some must be moved or removed to permit full relative articulation of the tractor-trailer bodies, while others often cannot reliably accommodate repeated articulation, particularly at large angles. Additionally, movable, inflatable and elastic panel systems, particularly if they require deployment controls, can add significantly to the cost of the tractor-trailer combination and they can be difficult to retro-fit to existing combinations. Such mechanical gap-spanning devices also often present problems when the trailer must be detached or separated from the tractor, which may be required several times a day in some applications.
Pressure drag on tractor-trailer combinations is not limited to the frontal area of the tractor and/or the gap disposed between the tractor and the articulating trailer. It is well known that the rear end of bluff bodies, such as trailers, are known to contribute significantly to aerodynamic drag as evidenced by the formation of a wake in the trailing region behind the trailer. The generation of the wake, formed by eddies can be contributed to the shape of the conventional trailer 24, which is essentially a rectangular box having a flat, rectangular roof 38 and matching floor 40, along with flat, rectangular side panels 42. The front and rear surfaces 44 and 46 of such trailers 24 are also generally flat rectangular surfaces. As such, current bluff bodies, such as trailers 24 suitable for use with tractors 20 of the Class 8 type, suffer from a low pressure zone at the rear 36 of the trailer 24 such that the airstream suffers from early separation, resulting in a broad eddying wake forming downstream of the separation. The net result is the creation of considerable aerodynamic drag.
Unfortunately, attempts to make the trailer shape more aerodynamic within the overall length of the trailer have been accompanied by reduced carrying capacity and interference during loading of the trailer. Additionally, attempts to make the rear of the trailer more aerodynamic, for example, by the addition of panels or inflatable bladders (not shown), can suffer from disadvantages such as added weight and a significant lengthening of the trailer, with associated reductions in fuel efficiency and more difficult handling characteristics.